The positron emission tomography (PET) tracer [F-18]GE-179 binds to the phencyclidine (PCP) site in the openN-methyl-D-aspartate receptor ion channel (NMDAR-IC). To demonstrate that PET can visualise increased [F-18]GE-179 uptake by active NMDAR-ICs and that this can be blocked by the PCP antagonist S-ketamine, 15 rats had an electrode unilaterally implanted in their ventral hippocampus. Seven rats had no stimulation, five received pulsed 400 mu A supra-threshold 60 Hz stimulation alone, and three received intravenous S-ketamine injection prior to stimulation. Six other rats were not implanted. Each rat had a 90 min [F-18]GE-179 PET scan. Stimulated rats had simultaneous depth-EEG recordings of induced seizure activity. [F-18]GE-179 uptake (volume of distribution, V-T) was compared between hemispheres and between groups. Electrical stimulation induced a significant increase in [F-18]GE-179 uptake at the electrode site compared to the contralateral hippocampus (mean 22% increase in V-T,p = 0.0014) and to non-stimulated comparator groups. Rats injected with S-ketamine prior to stimulation maintained non-stimulated levels of [F-18]GE-179 uptake during stimulation. In conclusion, PET visualisation of focal [F-18]GE-179 uptake during electrically activated NMDAR-ICs and the demonstration of specificity for PCP sites by blockade with S-ketamine support the in vivo utility of [F-18]GE-179 PET as a use-dependent marker of NMDAR-IC activation.